| As an effective device to suppress interference signal in the radio frequency(RF)communication front-end,filter occupies a lot of area in the system.The size of the whole system can be considerably reduced by optimizing both the number and size of filters.Taking both miniaturization and high performance into account is an important research direction of filter at present.At the same time,the switched filter banks and tunable bandpass filters are widely used in multiband and wideband communication systems.The main work of this thesis is as follows:1.Two substrate integrated waveguide(SIW)bandpass filters operating at 37-40 GHz are designed based on low temperature co-fired ceramics(LTCC)technology.The miniaturization of the substrate with high dielectric constant is realized by LTCC technology.The fourth-order SIW filter adopts the classical cascaded quadruplet(CQ)structure and generates a set of basically symmetric transmission zeros on both sides of the passband through capacitive cross coupling.In addition to using order to improve outof-band suppression,the fifth-order SIW filter also uses inductive cross coupling to introduce a transmission zero at high frequencies.The simulation results show that both filters have good performance.The fifth-order SIW filter is fabricated and tested,but the test results are worse than the simulation results.Based on error analysis,an optimization idea is proposed.2.The tunable filter is designed based on gallium arsenide(GaAs)pseudomorphic high electron mobility transistor(pHEMT)technology.The distributed combline structure,which loads the variable capacitor at the terminal,is used to realize the bandpass filter with adjustable center frequency.For the variable capacitance part,the on-chip variable capacitance is realized based on MOS tube and switched capacitor array.At the same time,space mapping is adopted to shorten the optimization time of microstrip line layout.The final design of the adjustable filter layout size is 1.76 mm(?)1.66 mm,can realize the center frequency 8-11 GHz continuous adjustable,frequency range can cover from 7.2-12.2 GHz,the adjustment range of 51.5%.In addition to good in-band performance,the four passbands produce a transmission zero at the high and low resistance bands respectively,with high out-of-band suppression.3.Based on GaAs pHEMT technology,the switched filter bank which occupies a large area is integrated on the chip to realize miniaturization.The 1.9-18 GHz wide band system is divided into seven band filters,and the switching channel is controlled by switching structure.A single-pole seven-throw(SP7T)switches is designed with a seriesparallel hybrid structure,which controls the turn-on or turn-off of a certain path through the high and low level loaded on the gate.According to the requirements of frequency band and out-of-band suppression of filters,seven filters of different frequency band are designed by flexible use of lumped and distributed parameter circuits,and each filter can achieve good in-band performance and out-of-band suppression effect.Filters of seven different frequency bands and the input and output switches are casculated through microstrip line structure matching,and the switch filter bank that meets the design specifications is obtained after overall optimization,and its layout size is 4.68 mm(?)4.82 mm. |
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